The present invention relates to instruments for testing sealed packages for burst strength; more particularly, the invention relates to an apparatus for calibrating such an instrument, to ensure that the instrument provides accurate and repeatable measurements.
One such instrument which may be used for flexible and rigid package testing is manufactured by the assignee of the present invention, under the designation SKYE Model 2000a. The SKYE Model 2000a is a microprocessor-controlled package test system that gives a measurement of package integrity and seal strength. The instrument may be used with a needle apparatus for puncturing the package to enable the instrument to selectively pressurize the interior volume to a predetermined amount, and to monitor the interior volume pressure, to determine whether the package can maintain a certain pressure without leaking, or to determine the actual burst pressure.
When the instrument is used for pressure burst testing of a package, a needle is first sealably penetrated into the package, and an air tube from the instrument is connected to the needle. The computer processor which is part of the instrument is set to gradually increase the air pressure inside the package, while monitoring the internal pressure. When the pressure rises to a value to cause the package to burst, the sudden drop in package internal pressure is monitored and recorded.
Burst testing is normally done by periodically removing a package from the assembly line, using some statistical sampling procedure, and using the instrument to ascertain whether the packages produced on the assembly line statistically meet the design requirements for the packages.
A problem in using such instruments can occur when more than one instrument is used for testing the same type of package on an assembly line, for even though each particular instrument produces accurate and repeatable measurement results, it is difficult to ensure that two or more different instruments will test to exactly the same absolute burst pressure value, because of variations between instruments and test set-ups. Likewise, when an instrument is used on many different days for the same package type testing, it is difficult to ensure that all packages tested on different days are being stressed to the same absolute pressure levels. What is needed is a test or calibration device which can be connected to any of a number of package burst detector instruments to ensure that all instruments are set to the same test conditions. The present invention meets this need, and provides a device for calibration of any test instrument to the same set of test conditions as any other similar test instrument.
The present invention comprises a device for calibrating a burst pressure detector for measuring burst pressure of packages, the device including a pressure container capable of being pressurized to predetermined pressures by the burst pressure detector via an input pressure port. A second port to the pressure container is connected to a pressure relief solenoid valve via an electrical pressure switch, which may be preset to any desirable burst pressure, which itself is electrically connected to a timer relay. When the pressure in the pressure container reaches the preset value of the pressure switch, the switch activates the timer and the timer activates the pressure relief solenoid valve, which vents the pressure from the pressure container to atmosphere. The timer continues to vent the pressure for the preset time of the timer, and then deactivates the pressure relief solenoid. A further port on the pressure container is connectable to a pressure sensor in the burst pressure detector, to enable the detector to monitor and record the burst pressure.
It is a principal object and advantage of the present invention to provide a calibration apparatus for the proper setup of package burst detectors.
It is another object and advantage of the present invention to provide a calibration and setup device to ensure that a plurality of package burst detectors can produce consistent and repeatable measurements.